The term “septal defect” generally refers to a perforation or other type hole (i.e., a defect) which passes through a thin wall of muscle or other tissue (i.e., a septum) which divides or separates “areas” within the body. Such defects can occur, either congenitally or by acquisition, between chambers of the heart (i.e., atrium or ventricle) or the great vessels (interatrial and interventricular septal defects or patent ductus arteriosus and aortico-pulminatry window respectively), causing shunting of blood through the opening.
Atrial septal defects were initially corrected by open heart surgery which required the surgeon to open the chest of a patient and bypass the heart temporarily (e.g., by means of a mechanical heart or a “heart-lung machine”). The surgeon would then physically cut into the heart and suture small defects closed. In the case of larger defects, a patch of a biologically compatible material would be sewn onto the septum to cover (i.e., “patch”) the defect. Balloon catheters, similar to that disclosed by Landymore et al. in U.S. Pat. No. 4,836,204, have been used by physicians to temporarily occlude septal defects, as a stabilizing measure, prior to implementation of corrective open heart surgical techniques.
To overcome limitations of surgical closure, a variety of interventional transcatheter closure techniques have been attempted. In such techniques, an occluding device is delivered through a catheter to the septal defect site. Once the closure device is positioned adjacent the defect, it must be attached to the rest of the septum in a manner which permits it to effectively block the passage of blood through the defect.
One such early closure device, U.S. Pat. No. 3,874,388 (King et al.), includes a pair of complex mechanical umbrellas, each having a plurality of arms extending radially from a central hub. The hubs of the two umbrellas are mechanically connected to one another and each umbrella includes a fabric covering over the arms, much like a common umbrella. The ends of each arm are provided with barbs which are anchored into the septum to hold the occluder in place. The complex umbrellas prove rather difficult to unfold after passage through a catheter, requiring an array of cables to deploy the arms. This makes proper placement of the device difficult, and the barbs on the arms prevent retraction or repositioning of the device once it is in place.
Although much progress has been made in the field since the King et al. device, heretofore known defect occluding systems, whether they be of a traditional atrial umbrella style (e.g., the ClamShell Septal Umbrella (ClamShell I, C.R. Bard, Inc.), the CardioSEAL device (Nitinol Medical Technologies, Inc.), the Sideris Buttoned Occluder (Sideris, U.S. Pat. No. 4,917,089), or the ASD Occlusion System (ASDOS, Dr. Osypka GmbH, Grenzach-Wyhlen, Germany), or other emerging plug style (e.g., The Monodisk System (Pavenik et al., U.S. Pat. No. 5,643,317), Angel Wings (Das, U.S. Pat. No. 5,578,045), the Amplatzer® Septal Occluder, or the HELEX Septal Occluder (W.L. Gore & Associates, Inc.), all suffer from a variety of common shortcomings.
These, and other such devices, generally rely on the caudal and cranial ends of the device being larger than the opening of the defect itself to physically trap the device across the opening. To accommodate transcatheter delivery techniques, the resulting device configurations have become unduly mechanical in nature, often including multiple components (e.g., ASDOS) and/or requiring the sequential delivery of device components, as well as the use of loading jigs (e.g., ASDOS, CardioSEAL) to prepare the device for insertion. Furthermore, many of these devices require assembly across the defect post delivery (e.g., ASDOS), thereby increasing the complexity of the transcatheter equipment, and delivery process, as for instance, by requiring two separate catheter entry points (e.g., ASDOS).
Further still, and of primary importance, heretofore known defect occluders do not optimally conform to the size (i.e., contour, dimensions and/or geometry) of the septal defect. Such devices therefore require great care in placement to ensure that the closure members entirely cover the defect. Because previously known devices typically use expanding frames to support the closure members that can straddle the opening of the defect, or otherwise become caught, complications may arise during implantation of such devices.
Generally, a great deal of remote manipulation and repositioning is required for proper device deployment because heretofore known defect occluder systems hold or retain the occluder in such a way that the device cannot be observed in its final, fully expanded position within the defect until the device is completely released. Extensive remote manipulation, such as by applying tension to one or more cables in order to deploy the arms of an umbrella, for instance, or to anchor the device in place, not only increases the difficulty of the procedure, but tends to increase the likelihood that the device will be improperly deployed, or suffer material fatigue leading to device strut fracture, a fundamental and well documented problem of the aforementioned umbrella type devices. Further still, the likelihood of retrieval of such devices post deployment is great, and in some cases retrieval is required so as to effectively occlude the defect and minimize the risk of embolization.
Occluder systems generally have either a single “hard point” connection (i.e., the occluder is held for deployment by a substantially rigid “hard point” connection until final release thereof within a defect), or a dual point connection, namely a hard point connection in combination with a “soft” secondary release mechanism (e.g., a release cord or suture used to provide emergency retrieval post hard point release). With the single hard point connection, a cyclical flexing of the occluder is possible therewith, however, once the hard point is disengaged from the occluder, further adjustment and retrieval is no longer possible.
For example, the Amplatzer® and ASDOS single hard point systems push the occluder from the catheter into the defect using an externally threaded rod (i.e., torquer catheter) that mates with a threaded nut, or the like, integral to the occluder, with release of the device thereafter once the occluder is adequately seated in the defect. A major shortcoming of this method is that the position of the catheter tip in the heart in relation to the fully deployed occluder usually pulls the occluder into an unintended, and unnatural position. This distorts the septum of the heart, and the physician must trust that upon release of the occluder from the delivery system, the septum will return to a natural position and the occluder will adequately seal the defect. The single hard point connection does not permit the physician to observe the occluder as it would sit naturally in the heart until it is released.
The dual point connection, which specifically addressed the shortcomings of the single hard point connection, provides a mechanism by which the occluder may be emergently retrieved in the case of mis-deployment after hard point release. The dual point CardioSEAL and HELEX systems permit the physician to better observe the occluder in a more “natural” condition or state, having previously disengaged the occluder from the single hard point connection, thereby effectively minimizing potential cardiac distortion. However, due to the nature of the soft point connection, no effective repositioning may be effectuated once the hard point connection has been disengaged without fear of damaging the occluder and thereby causing malfunction: only retrieval is possible should mis-deployment of the occluder be suspected. A further disadvantage to this method of occluder attachment is that occluder redeployment is not possible: having disengaged the hard point “control” connection, redeployment, in addition to repositioning, is no longer possible, with occluder retrieval via the soft point connection typically destroying the device. The soft point attachment is generally released by cutting the suture or cord at the rear of the delivery system, and drawing the full length of the suture from the occluder and through the entire delivery system—a procedure which effectively opens a fluid pathway from the rear of the delivery system into the area of the defect, especially of concern when occluding an atrial or ventricle defect, thereby creating attendant risks with such release arrangement and procedure.
It is, therefore, advantageous to provide a defect occluder system capable of reversibly retaining an occluder so as to be observable in its final position prior to release. More particularly, it is highly desirable to provide a delivery system release assembly which allows the device to free float in the defect, while maintaining the ability to reposition and or retrieve it, at any time prior to final release, without implicating occluder integrity. Further still, it is desirable to provide in a defect occluder delivery system a soft occluder release accomplished with reduced attendant patient risk, such as the elimination of problems associated with opening the fluid pathway from the rear of the delivery system into the heart.